On Copper.

229. Next to iron, Copper is more extensively used in the arts than any other metal. And of all the uses to which this metal has been applied of late years, none is of greater importance than that of sheathing for the bottoms of ships, to preserve the wood from injury by the water, and from destruction by marine animals. Its use in alloys is very great. It is not, however, intended here to enter into a general consideration of the advantages of copper and its compounds; these are sufficiently described in other works.

230. Copper was known and worked in the most remote ages. It is one of the commonest metals at the surface of the globe; and there are at least twenty-three varieties of its minerals. The ores common in this country are the yellow and grey sulphurets; the other ores may be regarded as mineralogical specimens. It ranks next to gold in the extent to which it is found in its metallic state; and in some condition it is found in almost all countries. The countries which are richest in this metal are England, Sweden, Austria, Saxony, Hungary, America, and Australia. Although copper was of very ancient use, it was not until the year 1689 that the art of extracting and refining the metal was revived in this country, — and this was principally in Cornwall: it appears to have been neglected from the time that the Saxons immigrated into this country.

231. The quantity of copper exported from this country, in 1850, in different states, as bricks, pigs, sheets, nails, sheathing, and other forms, was about 21,950 tons; there was imported into this country 45,930 tons of copper ore and regulus, and about 4,900 tons of unwrought and partially wrought copper.

232. Pure copper has a handsome red colour peculiar to itself; it posses metallic lustre in a high degree. It has a sensible taste; and when rubbed in the hand it communicates a very disagreeable and nauseous odour. It is highly malleable and ductile, and is an excellent conductor of heat and electricity. It does not take sharp impressions on being cast in moulds, and therefore is wrought for use chiefly by rolling and hammering. In moderately dry air its surface slowly acquires a brown tarnish, owing to a thin film of sub-oxide; and in a damp air it acquires a green crust, from the formation of the carbonate of copper.

233. The various processes of the manufacture of copper from the state of ore to its marketable state as a metal, are sufficiently described in other works. Mr. Vivian gave a very interesting account of those processes some years ago in the "Annals of Philosophy;" and the Article on Copper in Dr. Ure's "Dictionary of Arts and Manufactures," contains also much useful information. The following observations will therefore apply chiefly to the preparation and use of copper for the sheathing of ships.
234. The first use of this metal as a sheathing in the Royal Navy was in 1761, when the Alarm frigate was coppered as an experiment; a second ship was coppered in 1765; a third in 1770; a fourth in 1776; nine in 1777; and the remainder of the Royal Navy in the three following years.* But from the earliest use of this metal as a sheathing down to the present time considerable practical difficulties have presented themselves. At first it was found that the iron bolts which constituted the fastenings of the ship, below the water line as well as above, were speedily and greatly corroded, so that, after three or four years, ships were found to be unfit to be sent on foreign service. Some attempts were made to prevent the corrosion of the bolts; but when these failed, it appears that the Navy Board contemplated the discontinuance of copper sheathing, whilst the ships lay in ordinary. But before resolving on such a change, they suggested to the Master shipwrights and other professional offices of the dockyards, that mixed metal bolts in ships' bottoms would be less affected by the contact of copper than iron bolts would, and obtained their opinions in favour of such a change. The use of mixed metal bolts was, therefore, ordered about the year 1783, and the general use of copper was continued.

235. But whilst the corrosive action was excessive on the fastenings, the copper sheathing also was the subject to it. The corrosion of the copper was, however, so diversified, sometimes excessive in amount, and sometimes moderate, that all inquiry into the cause or causes of waste was for a long time baffled. There can be little doubt that it depended greatly on the manufacture of the metal, as the copper sheathing, manufactured at certain periods, was no less remarkable for its great durability than that manufactured at other periods was remarkable for the rapid wear to which it was subject. The following statistics will exemplify this statement: — In 1790, Mines Royal Copper, cold rolled, was put on the Argonaut, and when it was examined, in 1830, it was found to have sustained an annual loss of 1/280 part. Mines Royal Copper, also cold rolled, was put on the Roebuck, in 1794, and on the Bold in 1803, and, in 1811, each was found to have lost in weight 1/279 part annually.

236. The Metal Mills were, in the meantime, erected in Portsmouth dockyard, and the copper manufactured there seems to have varied very materially in quality. In 1815. the Snap was sheathed with copper manufactured there and, in 1821, its annual loss was found to have been 1/30. The Wellington was coppered with Portsmouth copper in 1816, and in 1824 its annual loss was found to have been 1/45 part. And the Latona was sheathed with Portsmouth copper in 1822, and the copper was examined in 1829, when it was found to have lost, annually, 1/12 of its weight. From about the date of the manufacture of the Lantona's copper great improvement is shown in the durability of the Portsmouth copper. The Amazon and the Ocean were sheathed in 1821; in 1837, the Ocean's copper was found to have lost 1/128 part annually; and in 1840 the Amazon's copper was ascertained to have lost, annually, 1/285. The copper sheathing, used in 1825, was durable in nearly the same degree; that used in 1826 and the two following years was less durable, the annual waste being 1/63, 1/67, 1/199, in particular examples. The sheathing used in 1831 lost, annually, in two examples respectively, 1/180 and 1/140. After that date numerous examples slow a diminished durability in the sheathing without any restoration of the good qualities which , at different periods before, had given it so extended a durability.

237. Now, although an important truth, in relation to the manufacture of copper, was involved in the suggestion of the Navy Board to the officers of the dockyards in 1783, it was not then perceived to apply to the manufacture of copper as it did to the condition of using the sheathing. The manufacture of copper at the metal mills in Portsmouth dockyard was conducted with great care by Mr. Vernon, who was master of that department for many years, and was performed with as great success as that of any copper whose use in the navy has been recorded, but he appears not to have been fully acquainted with some of the condition necessary to good copper sheathing. So far as the taking of assays during the process of refining the copper, he endeavoured to bring the metal into a good state; but until the subject was investigated by Sir Humphry Davy, it was not known what was the nature of the destructive action to which the copper as it is found in the state of sheathing, and to the means of diverting the action from the copper to some other substance whose destruction would be an inconsiderable loss in relation to that of the copper; so that the manufacture of copper was left untouched by his researches. The use of the cast-iron protectors; which be recommended, showed that the entire suspension of galvanic action in the sheathing was deemed even more injurious than the excessive waste of the metal, as the adhesion and growth of shell fish and marine vegetables became so great, that all ships were soon bad sailers after the protectors were put on. A condition of the sheathing is therefore required, that shall allow of only that degree of oxidation which will prevent the adhesion and growth of animals and vegetables, and thus keep the bottoms of ships clean, whilst the waste of metal shall not exceed the limit which is required to such an effect.

238. Experience in the navy has shown that copper may be manufactured for sheathing capable of very extended durability: the Mines Royal copper already mentioned was such; that was cold rolled; and some of the Portsmouth copper used as sheathing between the years 1820 and 1830, was about equal in durability, although not cold rolled. This would imply that the valuable condition in question, resulted no less from the chemical state of the purity of the metal, than from the mechanical processes which it passed through. The copper question, as it concerns the sheathing of ships in the navy, is therefore essentially a chemical question. This was in fact admitted when it was referred to the Royal Society in 1823, and the investigation was undertaken by Sir H. Davy; but about the time of the practical failure of his protectors, the decline of his health disabled him from the further prosecution of his inquiries into the subject: and since that period the application of chemistry in the manufacture of copper has not been deemed of importance. And whilst within these few years inquiries have been made into the character of copper of different manufacture by means of analysis, the results of these inquires have been retained perfectly distinct from the manufacture of the metal.

239. Various suggestions have indeed been offered as the result of such inquiries; — it has been observed that "the purity of copper is especially looked to" in the Netherlands, where the sheathing has been observed to be of excellent quality; and it has been suggested as desirable to produce a greater degree of solidity or closeness of the metal. The importance of these two conditions is undoubted; but how are they to be obtained, is the question. The Author has had occasion to propose that when the copper has been thoroughly purified, it should be definitely alloyed; and also that it should be cold rolled, that by these means the grain of the copper might be the more closely aggregated. It has been observed that cold rolled copper, which has worn uniformly, has kept clean as well as been durable, at all times preserving a smooth surface. But whatever improvement may result to good copper from cold rolling, it is certain this mechanical process will not answer as a substitute for badly manufactured copper; that which is intrinsically bad will remain so notwithstanding the rolling.

* Dr. Paris's Life of Sir H. Davy, Vol. II.
John Fincham: Outline of Ship-Building in Four Parts.Whittaker and Co., London, 1852. Part III, pp 61-64.